High strength alloys



June 16,1936. a. P. H ALLIWELL 2,044,165

HIGH STRENGTH ALLOYS Original Filed March 5, 1932 Vickers Hardn'ess Nu 40 so 120 1:50 zba 45a 5 00 850 lz oa [$00 2600 Ayez'ny 77me in Hour 5' v 8o Medium Carbon 25 6 Steel Q o zoo 460 660 a'oo Temperature in C.

WITNESSES: v INVENTOR Patented June 16, 1936 PATENT OFFICE HIGH STRENGTH ALLOYS George P. Halliwell, Pittsburgh, Pa., asslgnor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Original application March 3, 1932, Serial No.

Divided and this application December 1, 1934, Serial No. 755,573

5 Claims. (Ch 148-13) This invention relates to alloys and particularly to alloys having a high strength at elevated temperatures.

Iron and steel have been employed in industry as the component parts of power-plant apparatus, turbines, and turbine blades. Since the limiting temperatures and pressures at which such apparatus can be operated are governed largely by the tensile strength and proportional limit of the material from which they are fabricated, it is essential that the metal or alloy utilized shall have a high tensile strength and retain its initial dimensions under stress.

An object of this invention is to produce an alloy which has a high proportional limit and high tensile strength at normal and elevated temperatures.

Another object of this invention is to provide a process for producing alloys which will develop desired physical properties in the alloys.

This invention will be better understood by reference to the accompanying drawing, in which:

Figure 1 is a graph showing the hardness that may be imparted to alloys produced in accordance with the teachings of this invention by ageing the alloys at temperatures of 600 (3., 650 C. and 750 C.; and

Fig. 2 is a graph showing the percent. deflection at different temperatures for a given stress upon an alloy produced in accordance with the teachings of this invention as compared to certain known commercial alloys which have been stressed under the same conditions.

This application is a division of copending application Serial No. 596,565, filed March 3, 1932, and is directed to alloys containing cobalt, nickel, iron, titanium and chromium which are annealed within a predetermined temperature range, quenched and subjected to an ageing process at a lower temperature for different lengths of time in order to substantially improve the proportional limit and tensile strength of the alloy at normal and elevated temperatures.

The proportions of the constituents of the alloy may be varied over wide ranges, but in order that the-alloy may be forgeable, it is essential that the titanium content should be maintained below 10% while better results may be obtained where the titanium content is below 7%. The preferred range of the titanium content is between 2% and 5%. It is also desirable to maintain the nickel content of the alloy in substantial amounts to minimize oxidation and to improve the physical properties of the alloy at normal and elevated temperatures.

to 80%, the iron from 5% to the titanium from .5% to 10% and the chromium in amounts ranging from more than traces up to 25%. Carbon may also be present in limited amounts, but for most purposes it is maintained below 1%.

In the preferred embodiment of this invention, the base of nickel plus cobalt constitutes the major proportion of the alloy, and the amount of nickel is greater than the amount of cobalt. For example, alloys having high proportional limits and high tensile strength may be produced where the constituents of the alloy are within the following ranges: 40% to 60% nickel, 25% to 35% cobalt, 5% to 20% iron, 2% to 5% titanium, and 1% to 25% chromium.

In preparing the improved alloy, the nickel and cobalt are first melted together in a reducing or inert atmosphere and the additional alloying ingredients are then added. It is preferred to add the iron and titanium to the melt in the form of a term-titanium alloy containing approximate 1y iron and 25% titanium, though to obtaii. desired percentages of iron or titanium, additional amounts of either one of these metals may be added. After the melt is completed and just before casting, from one to two grams of a deoxidizer, such as alumimum'silicon, or manganese, is applied to a rod composed of nickel or a nickel-cobalt alloy and plunger into the molten bath. Care should be exercised in introducing the deoxidizer as it causes a rapid reaction of an ahnost explosive nature.

The alloys are cast and homogenized at 1000 C. for eight hours, then forgedand annealed at a temperature of from 900 C. to 1000 C. for approximately one hour and quenched from the annealing temperature. The quenching may be accomplished by subjecting the alloy to any suitable cooling medium such as air, oil or water. The alloys are then subjected to an ageing process at temperatures of from 500 C. to 800 C. for a period of time ranging from one-half to 2,000 hours.

The greatest improvement in the characteristics of the alloy which may be eflected by the ageing process may take place within the first few hours while about of the maximum increase in the hardness of the alloy is eiiected after an ageing of 72' hours. The time of ageing is also dependent upon the ageing temperature, for the ageing takes place in a shorter period of time at the higher temperatures. After the alloy has aged for a suflicient'time to produce the maximum hardness, the alloy is cooled.

Referring to the drawing and in particular to curves 3 of Figs. 1 and 2, the efiect of the heat treatment in accordance with the teachings of this invention are shown for a specific alloy comprising 49% nickel, 29.5% cobalt, 8.4% iron, 2.4% titanium, 9.5% chromium and .02% carbon.

In Fig. 1, the ordinate represents hardness as denoted by Vick'ers pyramid numerals and the abscissa represents time of ageing in hours. Curves 3 and 3' are illustrative of the hardness imparted to the same alloy which has been aged at temperatures of 600 C. and 750 C. respectively. Curves 9 and ii are illustrative of the hardness imparted to other specific alloys hereinafter identified as alloys Nos. 9 and 11 which are aged at different temperatures.

The increase in hardness of the alloy, as indicated by the curves, is undoubtedly caused at least partially by the precipitation of titanium either alone or as a compound of one or more of the alloying ingredients from solid solution through the ageing process. Experiments indicate, however, that unless substantial quantities of iron and cobalt are present, a pronounced increase in hardness will not be obtained at ageing temperatures.

Curve 3 in Fig. 2 is illustrative of a representative alloy produced in accordance with this invention and hereinafter identified. This curve indicates the superiority of these improved alloys in retaining initial dimensions under stress over medium carbon steel and a nichrome alloy containing approximately 60% nickel, 20% iron, 18% chromium and 2% manganese. This property is highly important in alloys employed for service at high temperatures.

In making tests to determine this characteristic, the alloys are first rolled down to a thickness of about .017 of an inch, cut into strips 5 inches in length heated at a temperature of 950 C. for a period of thirty minutes and cooled rapidly. The alloys are next subjected to the improved ageing process at a temperature of 650 C. for a period of 72 hours.

The fiat strips are then placed in a form of known radius ,and maintained thirty minutes at the desired temperature. After cooling, the strips are removed from the form and laid across two pivots placed four inches apart. The bending produced is measured by determining the radius of curvature'of the strip by means of a fixed micrometer at a point midway between the pivots. Since the curvature of the form is fixed, the vertical displacement in a four-inch form can be readily calculated. The percentage of maximum deflection, as illustrated by the curves in Fig. 2,

equals the vertical displacement of the strip after being constrained for the period and at the temperature indicated and then cooled, divided by the vertical displacement of the form and multiplied by 100.

Alloys comprising from 20% to 70% nickel, 10% to 60% cobalt, 5% to 60% iron, 2% to 5% titanium, and 1% to 20% chromium prepared in accordance with the teachings of this invention,

I and aged at 650 C. fora period of 72 hours have a proportional limit ranging from 45,000 to 80,000 pounds per square inch at room temperature and a proportional limit ranging from 30,500 to 66,250 pounds per square inch at a temperature 'of 600 C. The tensile strength of these alloys ranges from 135,000 to 170,250 pounds per square inch at room temperature and 92,000 to 127,100 pounds more than traces up to 20% chromium:

Composition Alloy number Nickel Cobalt Iron Titanium Chromium 40.0 29.4 0.5 2. 3 l3. 7 43. 9 29. 5 8. 4 2 4 9. 5 48.3 27.3 20.0 2. 7 0.3 46. l 24. 8 7. Z 1 18.7

When the above identified alloys are aged at a temperature of 650 C. for a period of '72 hours their physical properties at room temperature The high proportional limit of the improved alloys and their ability to retain their initial dimensions under stress renders them especially adaptable for use in apparatus which is subjected to high temperatures. It is to be noted that alloy #9 in the foregoing table has a high proportional limit of 66,250 pounds per square inch at a temperature of 600 C. and an elongation of 11%. Such valuable properties have not heretofore been approached in any known alloy, the highest previous value which has been obtained in cobaltnickel base alloys which have not been subjected to an ageing process being only 33,750 pounds per square inch. The marked improvement imparted to the alloys will, therefore, be readily appreciated.

The fact that the physical properties of these alloys are maintained at elevated temperatures renders them especially suitable for use as contacting portions of valves and valve seats for internal combustion engines or for valves of other machines or apparatus which are operated at comparatively high temperatures. Their high tensile strength and resistance to oxidation at comparatively high temperatures also renders them especially variable for use in springs and other apparatus.

While this invention has been described in detail with reference to specific examples, it is to be understood that it is not to be limited to the specific examples set forth in the foregoing disclosure, but that they should be construed as illustrative and not by way of limitation, and in view of the numerous modifications which may be eifected therein without departing from the spirit and scope of this invention, it is desired that only such limitations shall be imposed as are indicated in the appended claims.

I claim as my invention:

1. The process of improving the physical properties of an alloy consisting substantially of from 20% to 70% nickel, 60% to 10% cobalt, to 50% iron, .5% to titanium and chromium in amounts ranging from traces up to 20% which comprises quenching the alloy from a temperature or at least 900 C. and ageing the alloy at a temperature 01' 500 C. to 800 C. for a sumcient length of time toimprove the physical properties of the alloy.

2. The process or improving the physical properties or an alloy consisting substantially of from 40% to 60% nickel, 20% to 35% cobalt, 5% to 20% iron, 0.5% to titanium and chromium in amounts ranging from traces up to which comprises quenchingthe alloy from a temperature of at least 900 C. and ageing the alloy at a temperature of 500 C. to 800 C. for a sufficient length of time to improve the physical properties or the alloy.

3. An alloy consisting substantially of from 20% to 70% nickel, 60% to 10% cobalt, 5% to 50% iron, 0.5% to 10% titanium and chromium in amounts ranging from traces up to 20% which has been quenched from a temperature of at v least 900 C. and aged at a temperature of 500 to 800 C. for a sumcient length of time to improve the physical properties of the alloy.

4. An alloy consisting substantially o! from 40% to 60% nickel, 20% to cobalt, 5% to 20% iron, 0.5% to 10% titanium and chromium in amounts ranging from traces up to 20%, which has been quenched from a temperature of at least 900 C. and aged at a temperature of 500 C. to 800 C. for a suflicient length of time to improve the physical properties of the alloy.

5. An age hardened alloy consisting substantially or from to nickel, 30% to 24% cobalt, 5% to 10% iron, 2% to 5% titanium and 10% to 20% chromium, which has been quenched from a temperature or at least 900 C. and aged at a temperature of 500 C. to 800 C. for a suiflcient length of time to improve the physical properties of the alloy.

GEORGE r. W. 

